Light guide bodies which are based on the principle of embedding scattering particles in a transparent thermoplastic matrix are known.
For instance, EP 656 548 discloses light guide bodies which use polymer particles as scattering particles. More than 98% of the polymer particles have a size of at least 7 micrometers, and from 0.01 wt % (100 wt.ppm) to 1 wt % (10,000 wt.ppm) of them are added to a matrix plastic. These light guide bodies have the disadvantage that their weathering resistance is insufficient and they already exhibit cloudiness—expressed by the “haze” value—at a thickness of 1 mm, in particular above 2 mm.
EP 1453900 describes light guide bodies which contain barium sulphate with an average particle size of 0.3-20-micrometers as scattering particles in a concentration of 0.001 wt % (10 wt.ppm)—0.08 wt % (800 wt.ppm). These light guide bodies also have the disadvantage that they already exhibit cloudiness at a thickness of 1 mm, in particular above 2 mm.
The above-described light guide bodies of the prior art also have the disadvantage that a low luminance is achieved with observation perpendicular to the light emitting surface. Only at large angles, measured with respect to the surface normal of the light emitting surface (cf. FIG. 1), does the luminance increase significantly. This effect is represented in FIG. 2 for various scattering particles.
Besides light guide bodies comprising scattering particles, there are also light guide bodies which are produced by mechanical introduction of defects on the surface or by printing on the surface. Production of these light guide bodies, however, involves much greater production outlay. Furthermore, printing in particular causes poor transparency and therefore restricts the possibilities of the use of these light guide bodies. Light guide bodies having embedded scattering particles, conversely, can be produced economically by extrusion, injection moulding or by casting methods without post-processing. Examples of such printed light guide bodies may be found in JP2004351649, WO 2007/058060, WO 2009/137053, US 2005/272879.